Are u dumb? Japan is like a 🔥ing country full of overworked people, so much that in metropolitan areas, adult places can be found everywhere, and Japanese go there every Friday night to be freed from stress and this is a very common thing to them. Which means, they work early and overworked sometimes until 7pm-9pm in the evening.
That's why when they play mobile games they ave tendency to really get into it, and pour out a steady fat wad of cash just to relieve the stress at work. They're very competent when it comes to in-app purchases because they have the resources.